Method of preparing metal containing compounds using hydrodynamic cavitation

ABSTRACT

A process for the preparation of nanostructured materials in high phase purities using cavitation is disclosed. The method comprises mixing a metal containing solution with a precipitating agent and passing the mixture into a cavitation chamber. The chamber consists of a first element to produce cavitation bubbles, and a second element that creates a pressure zone sufficient to collapse the bubbles. The process is useful for the preparation of mixed metal oxide catalysts and materials for piezoelectrics and superconductors.

BACKGROUND OF THE INVENTION

[0001] Cavitation is the formation of bubbles and cavities within aliquid stream resulting from a localized pressure drop in the liquidflow. If the pressure at some point decreases to a magnitude under whichthe liquid reaches the boiling point for this fluid, then a great numberof vapor-filled cavities and bubbles are formed. As the pressure of theliquid then increases, vapor condensation takes place in the cavitiesand bubbles, and they collapse, creating very large pressure impulsesand very high temperatures. According to some estimations, thetemperature within the bubbles attains a magnitude on the order of 5000°C. and a pressure of approximately 500 kg/cm² (K. S Suslick, Science,Vol. 247, Mar. 23, 1990, pgs. 1439-1445). Cavitation involves the entiresequence of events beginning with bubble formation through the collapseof the bubble. Because of this high energy level, cavitation has beenstudied for its ability to mix materials and aid in chemical reactions.

[0002] There are several different ways to produce cavitation in afluid. The way known to most people is the cavitation resulting from apropeller blade moving at a critical speed through water. If asufficient pressure drop occurs at tile blade surface, cavitation willresult. Likewise, the movement of a fluid through a restriction such asan orifice plate can also generate cavitation if the pressure dropacross the orifice is sufficient. Both of these methods are commonlyreferred to as hydrodynamic cavitation. Cavitation may also be generatedin a fluid by the use of ultrasound. A sound wave consists ofcompression and decompression cycles. If the pressure during thedecompression cycle is low enough, bubbles may be formed. These bubbleswill grow during the decompression cycle and contract or even implodeduring, the compression cycle. The use of ultrasound to generatecavitation to enhance chemical reactions is known as Sonochemistry.

[0003] Both of these methods of cavitation to enhance mixing or aid inchemical reactions have had mixed results, mainly due to the inabilityto adequately control cavitation. U.S. Pat. Nos. 5,810,052, 5,931,771and 5,937,906 to Kozyuk disclose an improved device capable ofcontrolling the many variables associated with cavitation and the use ofsuch a device in Sonochemical type reactions.

[0004] Metal-based materials have many industrial uses. Of relevance tothe present invention are those solid state metal-based materials suchas catalysts, piezoelectric materials, superconductors, electrolytes,ceramic-based products, and oxides for uses such as recording media.While these materials have been produced through normal co-precipitationmeans, U.S. Pat. Nos. 5,466,646 and 5,417,956 to Moser disclose the useof high shear followed by cavitation to produce metal based materials ofhigh purity and improved nanosize. While the results disclosed in thesePatents are improved over the past methods of preparation, the inabilityto control the cavitation effects limit the results obtained.

SUMMARY OF THE INVENTION

[0005] Accordingly, the present invention is directed to a process forproducing metal based solid state materials of nanostructured size andin high phase purities utilizing controlled cavitation to both createhigh shear and to take advantage of the energy released during bubblecollapse.

[0006] The process generally comprises the steps of:

[0007] (a) mixing a metal containing solution with a precipitating agentto form a mixed solution that precipitates a product;

[0008] (b) passing said mixed solution at elevated pressure and at avelocity into a cavitation chamber, wherein said cavitation chamber hasmeans for creating a cavitation zone and means for controlling saidzone, and wherein cavitation of the mixed solution take place, forming acavitated precipitated product;

[0009] (c) removing said cavitated precipitated product and said mixedsolution from said cavitation chamber; and

[0010] (d) Separating said cavitated precipitated product from saidmixed solution.

[0011] The process according to the present invention preferably employsa special apparatus to carry out step (b) in the process. Such asuitable apparatus may be found in U.S. Pat. No. 5,937,906 to Kozyuk,which disclosure is incorporated by reference herein.

[0012] The present invention is particularly suitable for producingnanophase solid state materials such as metal oxides and metalssupported on metal oxides. The synthesis of nanostructured materials inhigh phase purities is important for obtaining pure metal oxides andmetals supported on metal oxides for applications in catalyticprocessing and electronic and structural ceramics. The synthesis of suchmaterials by hydrodynamic cavitation results in both nanostructuredmaterials as well as high phase purity materials due to the fact thatsuch processing results in high shear and high temperature localheating, applied to the synthesis stream components. High shear causesthe multi-metallics to be well mixed leading to the high phase puritiesand nanostructured particles, and the high in situ temperatures resultsin decomposition of metal salts to the finished metal oxides or metalssupported on metal oxides. The present invention may decompose at leastsome of the metal salts, and preferably all of the metal salts.

[0013] The advantage of the latter aspect is that materials produced bycontrolled cavitation do not require post synthesis thermal calcinationto obtain the finished metal oxides while conventional methods ofsynthesis requires a high temperature calcination step to decompose theintermediate metal salts such as carbonates, hydroxides, chlorides etc.Such steps are often exothermic and hazardous to accomplish on anindustrial scale.

[0014] The ability to synthesize advanced materials by hydrodynamiccavitation requires that the equipment used to generate cavitation havethe capability to vary the type of cavitation that is instantaneouslybeing applied to the synthesis process stream. The subject inventionutilizes controlled cavitation to efficiently alter the cavitationalconditions to meet the specifications of the desired material to besynthesized. The importance of the method is a capability to vary thebubble size and length of the cavitational zone, which results in abubble collapse necessary to produce nanostructured pure phasematerials. The correct type of bubble collapse provides a local shockwave and energy release to the local environment by the walls of thecollapsing bubbles which provides the shear and local heating requiredfor synthesizing pure nanostructured materials. The cavitation methodenables the precise adjustment of the type of cavitation forsynthesizing both pure metal oxide materials as well as metals supportedon metal oxides, and slurries of pure reduced metals and metal alloys. Afurther capability of the method, which is important to the synthesis ofmaterials for both catalysts and advanced materials for electronics andceramics, is the ability to systematically vary the grain sizes by asimple alteration of the process conditions leading to cavitation. Theimportance of this aspect of the technology is the well known phenomenathat many catalytic processes show reaction rates which are greatlyaccelerated by catalysts having grain sizes in the 1-10 run range.Furthermore, materials used in ceramic as well as structural ceramicsapplications have been observed to density at higher rates and to higherdensities when the starting materials can be synthesized in the optimumfine grain size.

[0015] The importance of the said described invention is that it is ageneral method of synthesis of nanostructured materials in high phasepurities while all known conventional methods of synthesis results inlower quality materials. The said invention has the capability tosynthesize single metal oxides in varying grain sizes of 1-20 nm,multimetallic metal oxides in varying grain sizes and as single phasematerials without the presence of any of the individual metal oxidecomponents of the desired pure materials situated on the surface of thedesired pure material. Furthermore, the synthesis of reduced metalssupported on metal oxides in both grain sizes of 1-20 nm and thecapability to vary the grain sizes between 1-20 nm is also possible. Dueto these unique capabilities, as compared to conventional methods ofsynthesis, the said method affords high quality catalysts, capacitors,piezoelectrics, novel titanias, electrical and oxygen conducting metaloxides, fine grains of slurries of finely divided reduced metals, andsuperconductors. Conventional methods of synthesis have demonstrated thecapabilities to synthesize some of these materials in high purity andfine grains; however, these processes have required a substantialadjustment in the chemistry of the synthesis of such materials. Theproblem with the conventional approach to the synthesis of high qualitysolid state materials is that the theory controlling precipitation andthe chemistry of synthesis is not well understood or controllable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows the variation in the strain and grain size of apiezoelectric as a function of orifice size; and

[0017]FIG. 2 is an XRD comparison of a piezoelectric prepared accordingto the present invention and by classical preparation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The apparatus utilized in the present invention consists of apump to elevate the pressure of the liquid being fed to the apparatus,and a cavitation zone within the apparatus. The cavitation zonecomprises:

[0019] (a) A flow-through channel having a flow area, internallycontaining at least one first element that produces a local constrictionof the flow area, and having an outlet downstream of the localconstriction; and

[0020] (b) A second element that produces a second local constrictionpositioned at the outlet, wherein a cavitation zone is formedimmediately after the first element, and an elevated pressure zone iscreated between the cavitation zone and the second local constriction.

[0021] The liquid is first pressurized, and then enters the flow-throughchannel. A local constriction in the channel creates an increase in thevelocity of the liquid flow to some minimum velocity, creating asufficient pressure drop to allow cavitation to occur. On average, andfor most hydrodynamic liquids, the minimum velocity is 16 m/sec orgreater.

[0022] The first element producing the local constriction may take manydifferent shapes. It may be of the form of a cone, or spherical orelliptical shape, and can be located in the center of the flow channel.It is possible to use a crosshead, post, propeller, nozzle or any otherfixture that produces a minor loss in pressure. Preferred is one or moreorifices or baffles. By varying the size of the orifice, the apparatusis able to better control the size of the cavitation bubbles beingformed. The orifice may have one or more circular or slotted openings.

[0023] The cavitation bubbles then are transported by the flow of liquidimmediately into a cavitation zone, which comprises numerous cavitationbubbles. The cavitation bubbles then flow with the liquid into anelevated pressure zone. By having a second element in the flow channeldownstream of the cavitation zone, a back pressure is created to formthe elevated pressure zone. The second element can also take manyshapes, but an element similar in operation to a control valve ispreferred. By controlling the pressure in this zone, the apparatus isable to determine the length of the cavitation zone and determine whenbubble collapse will occur. Upon entering the elevated pressure zone,the cavitation bubbles collapse, resulting in high pressure implosionswith the formation of shock waves that emanate from the point of eachcollapsed bubble. Under the high temperatures and pressures caused bybubble collapse, the liquid on the boundary of the bubble, and the gaswithin the bubble itself, undergo chemical reactions depending upon thematerials in the feed. These reactions may be oxidation, disintegrationor synthesis, to name a few.

[0024] In another aspect of the invention, the second element can be thefirst element of a second cavitation zone. In this manner two or morecavitation zones may be placed in series to produce a multi-stageapparatus. Each cavitation zone is controllable depending on the firstelement selected for the next cavitation zone, the distance between eachfirst and second element, and by the final second element at the end ofthe multi-stage apparatus.

[0025] In yet another aspect of the invention, the second element can beas simple as a extended length of the channel, a turn or elbow in thechannel, or another piece of processing equipment. The second elementmust provide some back pressure to create the cavitation and elevatedpressure zones.

[0026] The desired cavitated products are then removed from the liquidby suitable separation techniques, such as vacuum filtration, filtrationand evaporation. Prior to or after removal of the cavitated products,the liquid may be recycled back to the cavitation chamber. Recycle ofthe unfiltered product may occur many times. Where multi-stagecavitation chambers are used, recycle may be to one or more of thechambers. As the length of the period of recirculation increases, theresulting final product generally has a higher degree of phase purityand smaller particle size.

[0027] The nanostructured materials of the present invention aretypically prepared by precipitation of the desired product from a metalcontaining solution. The metal containing solution normally is aqueous,but can be non-aqueous. At least one component of the metal containingsolution must be in a liquid state and be capable of creatingcavitation. Other components may be different liquids, solids, gasps, ormixtures thereof. The liquid component could be materials commonlythought of as liquid, or can be materials commonly thought of as solidor gas being processed in their liquid state. Examples of such materialsare molten metals and molten minerals, as long as the vapor pressure issufficiently low enough to generate bubbles, and liquid carbon dioxide.

[0028] Most metals are in the form of salts. However, in the case ofcertain precious metals the metal may be added in the form of an acidsuch as chlorplatinic acid. Examples of suitable salts include nitrates,sulfates, acetates, chlorides, bromides, hydroxide, oxylates andacetylacetonates. The metal may be cobalt, molybdenum, bismuth,lanthanum, iron, strontium, titanium, silver, gold, lead, platinum,palladium, yttrium, zirconium, calcium, barium, potassium chronmium,magnesium, copper, zinc, and mixtures thereof, although any other metalmay find use in the present invention. For example, iron oxide may bemade from ferric nitrate hydrate, barium titanate from a mixture ofbarium acetate in water and titanium tetraisopropoxide in isopropylalcohol, and a ceramic such as lanthana from lanthanum nitrate. Complexmetal catalysts such as iron bismuth molybate may be formed utilizingthe appropriate metal salts.

[0029] A class of metals typically suited for piezoelectric, materialsare lanthanum, titanium, gold, lead, platinum, palladium yttrium,zirconium, zinc and mixtures thereof.

[0030] A class of metal typically suited for superconductors arestrontium lead, yttrium, copper, calcium, barium and mixtures thereof.

[0031] The solution into which the salt is dissolved will depend uponthe particular metal salt. Suitable liquids include water, aqueousnitric acid, alcohols, acetone, hydrocarbons and the like.

[0032] The precipitating agent may be selected from any suitable basicmaterial such as sodium carbonate, ammonium carbonate, potassiumcarbonate, ammonium hydroxide, alkali metal hydroxide or even waterwhere the metal salt reacts with water. Any liquid which causes thedesired metal salt to precipitate from solution due to insolubility ofthe metal salt in the liquid may be a precipitating agent.

[0033] In the embodiments where recycling occurs, it is desirable thatthe pH of the mixed solution be maintained on the basic side, usuallybetween 7.5-12. However, the range is dependent on the precise materialbeing synthesized.

[0034] In the case of preparing catalysts, a support may be addeddirectly to the metal containing solution, the precipitating agent orboth. Suitable supports include alumina, silica, titania, zirconia andalumino-silicates. The support may also be added in the form of a salt,such as alumina being added as aluminum nitrate hydrate where thesupport itself is precipitated in the form of nanostructured grainsimder cavitational conditions.

[0035] Zeolites such as ZSM-5, X-Type, Y-Type, and L-Type may beprepared using the process of the present invention. Metal loadedzeolitic catalysts typically contain a metal component such as platinum,palladium, zinc, gallium, copper or iron. The metal salt solution, theprecipitating agent and a silica source may be premixed to form azeolite gel prior to passing to the cavitation chamber. Where the gelrequires heat to form, the mixture may be recycled in the cavitationchamber until the gel forms and the synthesis results. Alternately,after cavitation, the well dispersed gel may be placed in a conventionalautoclave where a hydrothermal synthesis is carried out. This methodwill result in much finer grain zeolites after the conventionalhydrothermal treatment.

[0036] The process of the present invention has applicability tocatalysts, electrolytes, piezo-electrics, super-conductors and zeolitesas examples of nanostructured materials.

[0037] The following examples show the benefit of the present process inthe production of nanosize high purity products. Two apparatuses wereused in these examples. The Model CaviPro™ 300 is a two stage orificesystem operating up to 26,000 psi with a nominal flow rate of 300 ml/minand up. The CaviMax™ CFC-2h is a single orifice system operating up to1000 psi with a nominal flow rate of several liters per minute. Both ofthese devices are obtainable from Five Star Technologies Ltd, Cleveland,Ohio. Modifications were made to the peripheral elements of thesedevices, such as heat exchangers, cooling jacket, gauges and wettedmaterials, depending on the application contained in the examples.

EXAMPLE 1

[0038] This example illustrates that controlled cavitation enables thesynthesis of an important hydrodesulfurization catalyst for use in theenvironmental clean-up of gasoline in a substantially improved phasepurity as compared to conventional preparations. The preparation ofcobalt molybdate with a Mo/Co ratio of 2.42 was carried out in theCaviPro™ processor. Different orifice sizes were used for the experimentat a hydrodynamic pressure of 8,500 psi. In each experiment 600 ml of0.08M of ammonium hydroxide in isopropanol was placed in the reservoirand recirculated. While this precipitating agent was recirculated, amixture of 3.43 g (0.012 mol) of CoNO₃.6H₂O and 5.05 g (0.029 mol)(NH₄)₆Mo₇O₂₄.4H₂O dissolved in 50 ml of distilled water was metered inover 20 minutes. After the salt solution had been added, the resultingslurry was immediately filtered under pressure and dried for 10 hours at110° C. XRD analyses were recorded after air calcination at 325° C.

[0039] The conventional preparation of cobalt molybdate with a Mo/Coratio of 2.42 was carried out in classical synthesis. In each experiment600 ml of 0.08 M of ammonium hydroxide in isopropanol was placed in awell stirred vessel. While this precipitating agent was stirred, amixture of 3.43 g (0.012 mol) of CoNO₃.6H₂O and 5.05 g (0.029 mol)(NH₄)₆Mo₇O₂₄.4H₂O dissolved in 50 ml of distilled water was metered inover 20 minutes. After the salt solution had been added, the resultingslurry was immediately filtered under pressure and dried for 10 hours at110° C. XRD analyses were recorded after air calcination at 325° C.

[0040] The XRD pattern of the material after calcining in air indicates,by the high intensity of the reflection at 26.6 degrees 2θ in all of thesyntheses using cavitational processing, the formation of a highfraction of cobalt molybdate. Furthermore, the XRD of the conventionalmethod demonstrated a much lower intensity peak at 26.6 degrees 2θ aswell as strong reflections at 23.40 and 25.75 degrees 2θ due to separatephase MoO₃. Thus the present process produced a higher purity catalystthan found in the prior art.

EXAMPLE 2

[0041] The catalyst of Example I was repeated but at a higherhydrodynamic pressure of 20,000 psi. XRD patterns showed even higherphase purity as compared to the cavitation preparation in Example 1 andmuch better purity as compared to the classical synthesis.

EXAMPLE 3

[0042] The catalyst of Example 1 was prepared using a CaviMax processorat a lower pressure. The orifice used was 0.073 inches diameter at 580psi head pressure. The back pressure was varied between 0-250 psig. Thephase purity of cobalt molybdate was nearly as high as that observed inExample 2 and much better than that observed in Example 1. It was muchbetter than the conventional preparation that did not use hydrodynamiccavitation. The XRD data shows that the application of all backpressures resulted in higher purity phase of cobalt molybdate ascompared to the conventional preparation.

EXAMPLE 4

[0043] Example 1 was repeated using a CaviMax™ processor at a pressureof 200-660 psi. and using orifice sizes of 0.073, 0.075, 0.089, and0.095 inches diameter. The phase purities of the catalysts were allimproved. The use of an orifice diameter of 0.095 inches at 280 psiresulted in a superior quality hydrodesulfurization catalyst as comparedto all of the other diameters as well as the conventional synthesis.

EXAMPLE 5

[0044] This example illustrates the capability of the present inventionto synthesize high phase purities of cobalt molybdate supported ongamma-alumina. The synthesis of this material was carried out asfollows:

[0045] The preparation of cobalt molybdate deposited on gamma-aluminawith a Mo/Co ratio of 2.42 was carried out in the CaviPro™ processor. Acavitation generator having 0.009/0.010 inch diameter orifice sizes wasused for the experiment at a hydrodynamic pressure range of 4,000,7,000, and 8,000 psig. In each experiment 600 ml of a solution of0.0102% ammonium hydroxide in isopropyl alcohol (IPA) was placed in thereservoir along with 5.0 g of gamma-alumina, and the slurry wasrecirculated through the processor. While this precipitating agent wasrecirculated, 0.859 g (0.00295 mol) of Co(NO)₃.6H₂O and 1.262 g(0.000715 mole) of (NH₄)₆Mo₇O₂₄.4H₂O dissolved in 50 ml of water wasmetered in over 20 minutes. After all of the salt solutions had beenadded, the resulting slurry was recirculated through the processor foran additional 5 minutes. The slurry was immediately filtered underpressure and dried for 10 hours at 110° C. XRD analyses were recordedafter air calcination at 350° C. for four hours.

[0046] At all pressures the experiment resulted in superior phasepurities of the active hydrodesulfurization catalyst precursor, cobaltmolybdate, as compared to the conventional synthesis of the samecatalyst. In addition, for this catalyst, the optimum conditions for thegeneration of the smallest nanostructured grains of the catalystresulted from the low pressure, 4,000 psi synthesis.

EXAMPLE 6

[0047] The catalyst of Example 5 was prepared using silica in place ofalumina. The synthesis of this material was carried out as follows:

[0048] The preparation of cobalt molybdate deposited on Cabosil (silica)with a Mo/Co ratio of 2.42 was carried out in the CaviPro processor.Different orifice sizes were used for the experiment at a hydrodynamicpressure range of 10,000 psi. In each experiment 600 ml of 0.0102%ammonium hydroxide in isopropyl alcohol (IPA) was placed in thereservoir along with 5.0 g of Cabosil, and the slurry was recirculatedthrough the processor. While this precipitating agent was recirculated,0.859 g (0.00295 mol) of Co(NO)₃.6H₂O and 1.262 g (0.000715 mol) of(NH₄)₆Mo₇O₂₄.4H₂O dissolved in 50 ml of water was metered in over 20minutes. After all of the salt solutions had been added, the resultingslurry was recirculated through the processor for an additional 5minutes. The slurry was immediately filtered under pressure and driedfor 10 hours at 110° C. XRD analyses were recorded after air calcinationat 350° C. for four hours.

[0049] The cavitational synthesis resulted in higher phase purity forcobalt molybdate deposited on silica as compared to the conventionallyprepared catalyst, and the use of a 0.006 and 0.014 inch diameterorifice set led to finer nanostructured grains of the catalyst.

EXAMPLE 7

[0050] The present invention was used to synthesize beta-bismuthmolybdate (Bi₂Mo₂O₉), which is typical of the family of catalysts usedfor hydrocarbon partial oxidations such as the conversion of propyleneto acrolein or ammoxidation of propylene to acrylonitrile. Thissynthesis used a CaviMax™ processor with four different orifice sizes ina low pressure mode. The synthesis of this material was carried out asfollows.

[0051] 450 ml of IPA was used as the precipitating agent, and was placedin the reservoir. While this precipitating agent was recirculated, 12.83g, 0.0264 mol of Bi(NO₃)₃.5H₂O dissolved in 50 ml of 10% HNO₃, and 4.671g, 0.00378 mol of (NH₄)₆Mo₇O₂₄.4H₂O dissolved in 50 ml of distilledwater was metered in over 20 minutes. After all of the salt solutionshad been added, the resulting slurry was recirculated through theprocessor for an additional 2 minutes. The slurry was immediatelyfiltered under pressure and dried for 10 hours at 110° C. XRD analyseswere recorded after air calcination at 350° C. TABLE 1 Variation ofGrain Sizes Orifice Diameter Crystallite (in.) Grain Size (nm) 0.073 210.081 28 0.089 22 0.095 11

[0052] The cavitational syntheses all resulted in pure phasebeta-bismuth molybdate. Furthermore, the XRD patterns showed that thegrain size of the particles could be varied over a wide range ofmanometer sizes by changing the orifice sizes. Since it is well known inthe catalytic literature that manometer gains of catalysts often resultin greatly accelerated reaction rates, the capability of thecavitational syntheses to vary this grain size is of general importanceto several catalytic reactions other than hydrocarbon partial oxidation.

EXAMPLE 8

[0053] This example shows that the present invention as applied to thesynthesis of complex metal oxides such as perovskites and ABO₃ metaloxides results in unusually high phase purities not attainable byconventional methods of synthesis. The synthesis of this material wascarried out as follows:

[0054] The synthesis of La_(0.7)Sr_(0.3)FeO₃ was performed using aCaviMax™ processor and using orifice sizes of 0.073, 0.081, 0.089, and0.095 inch diameter. 600 ml of a 1M solution of Na₂CO₃ in distilledwater was placed in the reservoir, and the slurry was recirculatedthrough the processor. While this precipitating agent was recirculated,La(NO₃)₃6H₂O (7.999 g, 0.0185 mol), Fe(NO₃)₃.9H₂O (10.662 g, 0.0264 mol)and Sr(NO₃)₂ (1.6755 g, 0.00792 mol) were dissolved in 100 ml ofdistilled water and this solution was metered in over 20 minutes. Afterall of the salt solutions had been added, the resulting slurry wasrecirculated through the processor for an additional 5 minutes. Theslurry was immediately filtered under pressure and dried for 10 hours at110° C. XRD analyses were recorded after air calcination at 600° C.

[0055] The XRD data showed that an orifice size of 0.095 inches diameterresulted in the synthesis of nanostructured pure phase perovskite,La_(0.8)Sr_(0.2)Fe_(1.0)O_(3.0-x), as a nanostructured material of 18 nmand the phase purity was much better than that attainable by theconventional synthesis.

[0056] Parallel experiments using the CaviPro™ processor using orificesets of 0.006/0.008, 0.006/0.010, 0.006/0.012 and 0.006/0.014 inchdiameter all resulted in completely pure phases of the desiredperovskite containing no separate phase impurities. These results weresuperior to both the CaviMax™ and conventional synthesis. The importanceof this type of perovskite material is for CO oxidation in automotiveexhaust emissions applications, for solid state oxygen conductors forfuel cells applications, and for dense catalytic inorganic membranesused for oxygen transportation in the reforming of methane to syngas.

EXAMPLE 9

[0057] This example shows that strain can be systematically introducedinto a solid state crystallite by use of the present invention. Theexample examined the synthesis of titanium dioxide using the CaviMax™processor and examined the effect of strain introduced into the TiO₂crystal as the orifice size of the cavitation processor wassystematically changed. The synthesis of this material was carried outas follows:

[0058] 100 g (0.27664 mol) Ti-Butoxide was mixed with 2-Propanol to givea volume of 0.51 (Molarity=0.553 mol/l) in a glove-box under nitrogen.This process yielded a clear yellowish solution, which is stable in air.750 ml of deionized water was placed for a typical run in the reservoirof the CaviMax and circulated. 75 ml of the Ti-Butoxide/2-Propanolsolution was added slowly with a feed rate of 4 ml/minute. The solutionwith the precipitated Ti-compound was circulated for an additional 17minutes. Afterwards the slurry was high pressure filtered at 100 psi(6.9 bar). The filtrate was dried at 100° C. for 2 hours and thencalcined at 400° C. for 4 hours. The XRD data were taken after aircalcination and the percent strain was estimated from theWilliamson-Hall method. TABLE 2 Crystallite Strain Orifice Strain Size(inches) % 0.073 0.26 0.081 0.23 0.089 0.26 0.095 0.29 0.105 0.32 0.1150.33 0.230 0.43

[0059] As shown in Table 2, the strain content of the crystallitesincreased from 0.2% prepared with a small orifice (0.073 inchesdiameter) to 0.35% prepared with a large orifice (0.115 inchesdiameter), linear with its diameter. The ability to systematically alterthe strain within a crystallite is important due to the fact that itsystematically changes the chemical potential of the surface atoms whichis important to the application of these materials as photocatalysts andas optical absorbers.

EXAMPLE 10

[0060] The synthesis of 20% w/w Ag on titania of nanostructured metallicsilver was examined as a function of orifice size, and the results werecompared to the conventional synthesis of such metal supportedmaterials. The synthesis of this material was carried out as follows:

[0061] A precipitating agent consisting of 1000 ml of deionized waterwas recirculated in the CaviMax™ processor equipped with a 0.075 inchdiameter orifice. A 100 ml solution of titanium (IV) butoxide(Ti[O(CH₂)₃CH₃]₄) in isopropyl alcohol (0.63 mol/L Ti) was added to theCaviMax at 4 ml/min to form a precipitate. The total time ofprecipitation plus additional recirculation was 30 minutes. Immediatelyafterwards, two solutions were added simultaneously to therecirculating, precipitated titanium slurry. The first solutionconsisted of a 250 ml silver solution of silver acetate (AgOOCCH₃) indeionized water (0.046 mol/L Ag), which was added at a rate of 10ml/min. The second feed was a 250 ml solution of hydrazine (N₂H₄) inwater (0.70 mol/L N₂H₄), such that the N₂H₄/Ag molar ratio was 15.0,which was added at a rate of 10 ml/minute. The total time of additionplus additional recirculation was 30 minutes. The product was filtered,washed with water to form a wet cake, and then dried in an oven at 110°C. A portion of the dried product was calcined in air for 4 hours at400° C. A portion of the dried product was submitted for x-ray analysisand identified as silver on an amorphous titanium support. X-ray linebroadening analysis indicated that the mean silver crystallite size was7.4 nm. A portion of the calcined product was submitted for x-rayanalysis and identified as silver on titania. All of the titania wasidentified as anatase, while no rutile was observed. X-ray linebroadening analysis indicated that the mean silver crystallite size was12.0 nm. The conventional synthesis was performed as above except in astirred 1500 ml beaker.

[0062] The grain sizes of the silver particles after drying the samplesat 110° C. are shown in Table 3. This example shows that metallicparticles deposited on reactive supports such as titania can besynthesized in smaller grain sizes as compared to parallel conventionalsynthesis. Furthermore, when the catalysts were calcined to 400° C. inair, the silver particles deposited on the conventional catalyst grew toa much larger size than those deposited by cavitational techniques.These types of materials are important as photocatalysts for thedestruction of toxins in waste chemical streams. TABLE 3 Grain Size of20% w/w Silver on Titania Grain size, dried Gram Size, Calcined (nm)400° C. Conventional Precipitation- 7.6 20.1 Deposition CaviMax 0.115orifice 4.7 13.4 CaviMax 0.073 orifice 7.4 12.0

EXAMPLE 11

[0063] 2% w/w silver was synthesized on alpha-alumina using both acavitational synthesis and a conventional synthesis. The synthesis ofthis material was carried out as follows.

[0064] A slurry consisting of 5.00 g of aluminum oxide (alpha, Al₂O₃) in1000 ml deionized water was recirculated in the CaviMax processorequipped with a 0.073 inch diameter orifice. Two solutions were added tothe recirculating aluminum oxide slurry. The first solution consisted ofa ml solution of silver acetate (AgOOCCH₃) and ammonium hydroxide(NH₄OH) in deionized water. The concentration of the silver was 0.0095mol/L, and the concentration of ammonium hydroxide was 0.095 mol/L, sothat the NH₄OH/Ag molar ratio was 10.0. The silver solution was added tothe aluminum oxide slurry at a rate of 4 ml/minute. The second feed wasa 100 ml solution of hydrazine (N₂H₄) in water (0.14 mol/L N₂H₄), suchthat the N₂H₄/Ag molar ratio was 15.0, which was added at a rate of 4ml/minute. The total time of addition plus additional recirculation was30 minutes. The product was filtered, washed with water to form a wetcake, and then dried in an oven at 110° C. A portion of the driedproduct was submitted for X-ray analysis and identified as silver onalpha alumina. Conventional synthesis was performed in the same manneras above except in a stirred 1500 ml beaker.

[0065] The data in Table 4 show that the cavitational synthesis using anorifice size of 0.073 in. diameter and a 10/1 NH₄OH/Ag ratio resulted inmuch smaller grain sizes of Ag. TABLE 4 Grain sizes (nm) of 2% Ag/Al₂O₃synthesis 2% Ag/titania 10:1 NH₄OH:Ag Conventional Synthesis 20.9 nmgrains CaviMax 0.073 in. dia. 14.0 nm grains

EXAMPLE 12

[0066] The present invention was utilized for the synthesis ofnanostructured particles of gold supported on titanium oxide (TiO₂). Thesynthesis of this material was carried out as follows:

[0067] A precipitating agent consisting of 650 ml of deionized water wasrecirculated in the CaviMax™ processor equipped with a 0.075 inchdiameter orifice. A 100 ml solution of titanium (IV) butoxide(Ti[O(CH₂)₃CH₃]₄) in isopropyl alcohol (0.88 mol/L Ti) was added to theCaviMax™ at 4 ml/minute to form a precipitate. The total time ofprecipitation plus additional recirculation was 37.75 minutes.Immediately after, two solutions were added simultaneously to therecirculating, precipitated titanium slurry. The first solutionconsisted of a 1000 ml gold solution of chloroauric acid (HAuCl₄ 3H₂O)in deionized water (0.0073 mol/L Au), which was added at a rate of 4.7ml/minute. The second feed was a 100 ml solution of hydrazine (N₂H₄) inwater (0.12 mol/L N₂H₄), such that the N₂H₄/Au molar ratio was 16.7,which was added at a rate of 0.4 ml/minute. The total time of additionplus additional recirculation was 3.62 hours. The product was filtered,washed with water to form a wet cake, and then dried in an oven at 110°C. A portion of the dried product was calcined in air for 4 hours at400° C. A portion of the calcined product was submitted for x-rayanalysis and identified as gold on titania (anatase). X-ray linebroadening analysis indicated that the mean gold crystallite size was7.5 nm, and that the mean anatase crystallite size was 12.9 nm.Conventional synthesis was prepared in the manner above except in astirred 1500 ml beaker.

[0068] The data in Table 5 shows that cavitational processing during thesynthesis of 2% w/w of gold on titania results in systematicallydecreasing, grain sizes into the very small manometer size range. Thisexample shows that the combination of orifice size selection and processparameters afford a control of grain sizes not possible withconventional synthesis. TABLE 5 Grain size as a function gold solutionvolume Gold Volume of H₂NNH₂ Titania Gold grain conc. Au soln. feed rategrain size size (mol/L) (mL) (mL/min) (nm) (nm) 0.0145  50 8.0 12.5 78.60.0073 100 4.0 11.6 33.6 0.0036 200 2.0 11.4 27.9 0.0018 400 1.0 12.016.0 0.0007 1000  0.4 12.9  7.5

[0069] Where cavitation synthesis gave a 16 nm Au grain size,conventional synthesis resulted in a grain size of 25 nm. Wherecavitation synthesis gave a 7.5 nm Au grain size, conventional synthesisgave a grain size of 23 nm.

EXAMPLE 13

[0070] The present invention was used to synthesize commerciallyimportant piezoelectric solid state materials in very high phasepurities at low thermal treating temperatures. TABLE 6 Preparation ofPZT in different stoichiometries Ratio ZrBut TiBut Sum Zr:Ti [ml] [ml]formula 30:70 15 35 Pb(Zr_(0.3)Ti_(0.7))O₃ 40:60 20 30Pb(Zr_(0.4)Ti_(0.6))O₃ 50:50 25 25 Pb(Zr_(0.5)Ti_(0.5))O₃ 60:40 30 20Pb(Zr_(0.6)Ti_(0.4))O₃

[0071] Four solutions were prepared to synthesize PZT. 105.95 g (0.279mol) Pb(II)acetate trihydrate (PbAc) were dissolved in 1000 ml purifiedwater. 100 g (0.279 mol) Ti-Butoxide (TiBut, 97%) were diluted with2-Propanol to 500 ml. 132.58 g (0.279 mol) Zr-Butoxide-Butanol-Complex(ZrBut, 80%) was diluted with 2-Propanol to 500 ml. 2.74 g (0.0285 mol)of ammonium carbonate (Amm) was solved for each run in 350 ml water togive a 0.0814M solution. The detailed stoichioinetric information forthis series is given in Table 6. The ammonium carbonate solution wasplaced in the reservoir and circulated. The Zr and Ti solutions werecombined and fed at a rate of 2.5 ml/minute into the reservoir stream ata position just before the inlet to the high pressure, pump. ThePb-acetate solution was co-fed with a rate of 5 ml/minute. All of themetal containing components immediately precipitated and were drawn intothe high pressure zone of the cavitation processor and then passed intothe cavitation generation zone. All samples were dried over night andcalcined in three steps for four hours at 400° C., 500° C. and 600° C.

[0072] XRD patterns illustrated that above a calcination temperature of500° C. only the pure perovskite phase is formed with no lead oxide orzirconium oxide impurities. The XRD patterns contains some finercrystallites of this material appearing as a broad band centered at 30degrees 20. This material disappears from the composition aftercalcination to 600° C.

[0073] Furthermore, this type of material showed a much higher phasepurity than the classical method of preparation in which only vigorousmechanical stirring was done during the co-precipitation step. The datain FIG. 1 illustrates that the hydrodynamic cavitation technique enablesthe synthesis of piezoelectrics in compositions having a very highdegree of strain built into the individual crystallites. Furthermore,FIG. 1 shows that the degree of strain can be systematically introducedinto the crystals as a function of the type of orifice used in thesynthesis. It was found that the degree of strain introduced bycavitation was much greater than that found in a classical method ofpiezoelectric synthesis of the same composition.

[0074] The data in FIG. 2 illustrates the advantage of cavitationalprocessing in PZT synthesis by a direct comparison to a classicalco-precipitation synthesis. The top XRD pattern in FIG. 2 resulted froma cavitational preparation after 600° C. air calcination. The lowerfigure resulted from a classical co-precipitation carried out using thesame synthesis procedure except that only high speed mechanical stirringwas used in the co-precipitation step rather than cavitationalprocessing. A comparison of the two XRD patterns shows that theclassical pattern has a substantial fraction of separate phase leadoxide while the cavitational preparation has no secondary phase in itscomposition. This higher phase purity is exceptionally important to thefunctioning of the materials as a piezoelectric device.

EXAMPLE 14

[0075] The present invention was utilized for the synthesis of fineparticles of pure metallic particles in a slurry where the grain sizecan be altered depending upon the orifice sizes being used. The data inTable 7 illustrates the capability to form nanostructured grains offinely divided metals typically used commercially to hydrogenatearomatics and functional groups on organic intermediates in finechemical and pharmaceutical chemical processes. The synthesis of thismaterial was carried out as follows:

[0076] Hexachloroplatinic acid was dissolved 0.465 g in 50 mlisopropanol. This platinum solution was fed to a stirred Erlenmeyerflask, containing 0.536 g hydrazine hydrate, 54.7% solution in 50 mlisopropanol. The platinum solution feed rate was 5 ml/minute. Directlyfollowing the platinum reduction, the solution was fed to the CaviProprocessor, and processed for 20 minutes, after which time the XRD of thedried powders were measured. TABLE 7 Effect of pressure and orificesizes on the synthesis of nanostructured platinum Orifice set PressurePt metal grain size (nm) .004/.014 25,000 psi 3.9 .004/.006 25,000 psi3.7 .004/.014 15,000 psi 4.1 .004/.006 15,000 psi 3.9 Classical   14.7psi 5.4

EXAMPLE 15

[0077] The process of the present invention was used to fabricate thecommercially important silver on a-alumina catalysts used in theproduction of ethylene oxide from the partial oxidation of ethylene. Thedata in Table 8 illustrates the XRD determined grain sizes of the silverparticles which had been deposited onto a-alumina during thecavitational synthesis in which the silver was reduced in a cavitationexperiment and then deposited onto the a-alumina in water usingclassical techniques. The data shows that changing the orifice sizesused in each experiment can alter the grain size of the silver. Thecharacteristics of the different orifice sizes are expressed as thethroat cavitation numbers calculated for each experiment, which is acommon reference for the occurrence of cavitation in flowing fluidstreams. Using this method of characterization, the cavitation generatedin the metal synthesis stream is higher as the throat cavitation numbersdecreases.

[0078] The synthesis of this material was carried out as follows:

[0079] 2% silver on α-alumina was prepared by the reduction of silveracetate using hydrazine. This reduction was conducted in the CaviPro™processor at a pressure of 15,000 psi, followed by a classicaladsorption/deposition of an aqueous slurry of silver particles onto analpha-alumina support. The number of passes of the medium for eachconsecutive experiment was fixed, and the feed flow rates and processingtime were adjusted accordingly. The total number of passes for thisseries of experiments was held constant at 17.6. Experiments wereconducted at varying throat cavitation number, by varying the size ofthe first orifice. TABLE 8 Variation in silver particle grain sizesOrifice Sets Throat Cavitation Number Silver in./in. (calculated) Grainsize (nm) 0.005/0.014 3.07 16.00 0.007/0.014 4.36 21.00 0.009/0.014 5.4619.20 0.011/0.014 7.93 17.30

EXAMPLE 16

[0080] The degree of calcination was examined when using the presentinvention. Four separate samples of solid ammonium molybdate werecalcined for four hours in air to 100° C., 175° C., 250° C. and 325° C.respectively. XRD data was then taken for each sample. A sample ofammonium molybdate was dissolved in water and fed into an isopropylalcohol solution (the precipitation agent) just before it passed into aCaviPro™ processor using a 0.012/0.014 inch orifice set. This sample wasthen filtered and dried at 100° C. XRD data was then obtained for thissample. A comparison of the XRD patterns showed that the samplegenerated from the present invention had a degree of calcination greaterthan the sample calcined at 100° C., and about equal to that of the 175°C. sample. Considering the residence time of milliseconds for thepresent invention as compared to 4 hours for the conventional method,the use of the present invention resulted in some in situ thermalcalcination.

We claim:
 1. A process for the preparation of nanostructured materialsin high phase purities comprising: a) mixing a metal containing solutionwith a precipitating agent to form a mixed solution that precipitates aproduct; b) passing the mixed solution at elevated pressure and at avelocity into a cavitation chamber, wherein said cavitation chamber hasmeans for creating a cavitation zone and means for controlling saidzone, and wherein cavitation of the mixed solution takes place, forminga cavitated precipitated product; c) removing the cavitated precipitatedproduct and the mixed solution from the cavitation chamber; d)separating the cavitated precipitated product from the mixed solution.2. The process of claim 1 wherein at least some precipitation of themixed solution occurs in step (b).
 3. The process of claim 1 whereinboth high shear and at least some in situ calcination of the mixedsolution occur in the cavitation chamber.
 4. The process of claim 1wherein the cavitation chamber comprises: a) a flow-through channelhaving a flow area, internally containing at least one first elementthat produces a local constriction of the flow area, and having anoutlet downstream of the local constriction; b) a second element thatproduces a second local constriction positioned at the outlet, wherein acavitation zone is formed immediately after the first element, and anelevated pressure zone is created between the cavitation zone and thesecond local constriction.
 5. The process of claim 4 wherein thevelocity of the mixed solution passing into the cavitation chamber is ata velocity sufficient to create cavitation bubbles to form downstream ofthe first element.
 6. The process of claim 5 wherein the cavitationbubbles are formed in the cavitation zone, and the cavitation bubblescollapse in the elevated pressure zone.
 7. The process of claim 5wherein the first element is selected from the group consisting of atleast one orifice, a cone, a spherical shaped body, a elliptical shapedbody, and at least one baffle.
 8. The process of claim 7 wherein theorifice is selected from the group consisting of a orifice having acircular opening and a orifice having a slotted opening.
 9. The processof claim 5 wherein the second element is selected from the groupconsisting of a gate valve, a ball valve, a orifice and a length of theflow channel, wherein the length creates a hydraulic resistance.
 10. Theprocess of claim 5 wherein the second element has means for controllingthe pressure in the elevated pressure zone.
 11. The process of claim 10wherein the means is a control valve.
 12. The process of claim 10wherein the cavitation zone has a length, and wherein the means forcontrolling the pressure in the elevated pressure zone additionallycontrols the length of the cavitation zone.
 13. The process of claim 4having two or more cavitation chambers in series.
 14. The process ofclaim 13 wherein the first element of the succeeding chamber is thesecond element of the preceding chamber.
 15. The process of claim 5wherein the metal containing solution is a metal salt solution.
 16. Theprocess of claim 15 wherein the metal salt is selected from the groupconsisting of nitrate, acetate, chloride, sulfate, bromide, and mixturesthereof.
 17. The process of claim 15 wherein the metal in the metalcontaining solution is selected from the group consisting of cobalt,molybdenum, bismuth, lanthanum, iron, strontium, titanium, silver, gold,lead, platinum, palladium, yttrium, zirconium, calcium, barium,potassium, chromium, magnesium, copper, zinc, and mixtures thereof. 18.The process of claim 17 wherein the metal in the metal containingsolution is selected from the group consisting of cobalt, molybdenum,bismuth, iron, potassium, and mixtures thereof.
 19. The process of claim18 wherein the metals are bismuth and molybdenum.
 20. The process ofclaim 18 wherein the metals are cobalt and molybdenum.
 21. The processof claim 17 wherein the metal in the metal containing solution isselected from the group consisting of lanthanum, titanium, gold, lead,platinum palladium, yttrium, zirconium, zinc and mixtures thereof. 22.The process of claim 21 wherein the metal is titanium.
 23. The processof claim 21 wherein the metal is gold.
 24. The process of claim 17wherein the metal in the metal containing solution is selected from thegroup consisting of strontium, lead, yttrium, copper, calcium, bariumand mixtures thereof.
 25. The process of claim 17 wherein the mixedsolution additionally contains a solid support.
 26. The process of claim25 wherein the support is selected from the group consisting of alumina,silica, and titania.
 27. The process of claim 5 wherein said mixedsolution additionally contains a source of silica and the so formedmixed solution is a zeolite gel.
 28. The process of claim 5 wherein saidmixed solution of step (c) is recycled to said cavitation chamber. 29.The process of claim 28 wherein the precipitating agent is added to themixed solution as it is recycled.
 30. The process of claim 28 whereinthe metal containing solution is added to the mixed solution as it isrecycled.
 31. The process of claim 17 wherein the cavitated precipitatedproduct is a catalyst.
 32. The process of claim 31 wherein the cavitatedprecipitated product is a catalyst containing at least bismuth andmolybdenum.
 33. The process of claim 31 wherein the cavitatedprecipitated product is a catalyst containing at least cobalt andmolybdenum.
 34. The process of claim 21 wherein the cavitatedprecipitated product is a piezoelectric.
 35. The process of claim 24wherein the cavitated precipitated product is a superconductor.
 36. Aprocess for the preparation of nanostructured materials in high phasepurities comprising: a) mixing a metal containing solution with aprecipitating agent to form a mixed solution that precipitates aproduct; b) passing the mixed solution at elevated pressure into acavitation chamber to create cavitation thereby forming a cavitatedprecipitated product, said cavitation chamber includes: i) means forcreating a cavitation zone, and ii) means for controlling saidcavitation zone by providing adjustable back pressure within saidcavitation zone; c) removing the cavitated precipitated product and themixed solution from the cavitation chamber; and d) separating thecavitated precipitated product from the mixed solution.
 37. The processof claim 36, wherein at least some precipitation of the mixed solutionoccurs in step (b).
 38. The process of claim 36, wherein both high shearand at least some in situ calcination of the mixed solution occur in thecavitation chamber.
 39. The process of claim 36, wherein said means forcreating said cavitation zone includes a first element internallysituated within a flow-through channel having a flow area wherein saidfirst element produces a local constriction of the flow area, saidcavitation zone is formed immediately after said first element.
 40. Theprocess of claim 36, wherein said cavitation chamber further comprisesmeans for creating a second cavitation zone to produce a multi-stageprocess.
 41. The process of claim 40, wherein said means for creatingsaid second cavitation zone includes a second element internallysituated within said flow-through channel having a second flow areadownstream of said first element wherein said second element produces asecond local constriction of the second flow area, said secondcavitation zone is formed immediately after said second element.
 42. Theprocess of claim 41, wherein said means for controlling said cavitationzone is varying the distance between the first and second element toprovide adjustable back pressure within said cavitation zone.
 43. Theprocess of claim 41, wherein said means for controlling said cavitationzone is the second local constriction produced downstream of said firstelement thereby providing adjustable back pressure within saidcavitation zone.
 44. The process of claim 41, wherein said cavitationchamber further comprises means for controlling said second cavitationzone to produce a multi-stage process.
 45. The process of claim 44,wherein said means for controlling said second cavitation zone includesa third element internally situated within said flow-through channeldownstream of said second element to produce a third local constrictiondownstream of said second element thereby providing adjustable backpressure within said cavitation zone.
 46. The process of claim 39,wherein said means for controlling said cavitation zone includes asecond element internally situated within said flow-through channeldownstream of said first element to produce a second local constrictionthereby providing adjustable back pressure within said cavitation zone.47. The process of claim 46, wherein said means for controlling saidcavitation zone creates an elevated pressure zone between saidcavitation zone and said second local constriction.
 48. The process ofclaim 46, wherein said second element is a control valve.
 49. A processfor the preparation of nanostructured materials in high phase puritiescomprising: a) mixing a metal containing solution with a precipitatingagent to form a mixed solution that precipitates a product; b) passingthe mixed solution at elevated pressure and at a velocity into acavitation chamber to create cavitation thereby forming a cavitatedprecipitated product, said cavitation chamber includes: i) means forcreating a cavitation zone, and ii) means for controlling saidcavitation zone by providing back pressure within said cavitation zone;c) removing the cavitated precipitated product and the mixed solutionfrom the cavitation chamber; and d) separating the cavitatedprecipitated product from the mixed solution.
 50. The process of claim49, wherein at least some precipitation of the mixed solution occurs instep (b).
 51. The process of claim 49, wherein both high shear and atleast some in situ calcination of the mixed solution occur in thecavitation chamber.
 52. The process of claim 49, wherein said means forcreating said cavitation zone includes a first element internallysituated within a flow-through channel having a flow area wherein saidfirst element produces a local constriction of the flow area, saidcavitation zone is formed immediately after said first element.
 53. Theprocess of claim 49, wherein the velocity of the mixed solution passinginto the cavitation chamber is at a velocity sufficient to createcavitation bubbles to form downstream of the first element.
 54. Theprocess of claim 52, wherein said means for controlling includes asecond element internally situated within said flow-through channeldownstream of said first element to produce a second local constrictionthereby providing back pressure within said cavitation zone to create anelevated pressure zone between said cavitation zone and said secondlocal constriction.
 55. The process of claim 54, wherein the cavitationbubbles are formed in said cavitation zone and the cavitation bubblescollapse in the elevated pressure zone.
 56. The process of claim 55,wherein the second element provides adjustable back pressure within saidcavitation zone to control said elevated pressure zone.
 57. The processof claim 56, wherein the second element is a control valve.
 58. Theprocess of claim 49, further comprising a second cavitation chambersituated in series with said cavitation chamber.